In recent years, addition of various nanomaterials has been studied for purposes of downsizing and weight saving in various fields. In particular, for problems of environments or resources, carbon materials such as graphene, CNT (carbon nanotube) and fullerene have attracted attention as nonmetal nanomaterials.
For example, although carbon black has been used as a conductive assistant for lithium-ion batteries and the like, carbon nanofiber VGCF (registered trademark) manufactured by Showa Denko K.K., etc. have been studied in recent years to further secure conductivity (Patent Literature 1).
Among them, graphene is superior to other carbon materials in aspect of mass productivity, handleability, etc., as well as performance, and expectations have been placed on graphene in various fields.
In order to obtain high-quality graphene which, for example, has fewer graphite layers, a method in which weak ultrasonic waves are applied to natural graphite in a solvent (NMP) for a long time (7-10 hours), large agglomerates which deposit on the bottom are then removed, and the supernatant is then centrifuged to concentrate it, thereby obtaining a graphene dispersion in which 20% or more of flakes of a single layer, 40% or more of flakes of double or triple layers, and less than 40% of flakes of 10 layers or more of a graphite material are dispersed at about 0.5 g/L, has been considered (Patent Literature 2).